The invention pertains to a process for the continuous thermal separation of mixed substances, especially of solutions, suspensions and emulsions.
The industrial production of mixed substances, especially, however by no means exclusively, of polymers, especially homo- and co-elastomers, occurs due to polymerization reactions in the so-called solution-polymerization process, in which process the viscosity inside the mixer boiler reactor is lowered through the use of solvents, in order to achieve a more even mixture. From the polymer solution formed in this process, the solvent needs to be separated. The removal of this diluent has until now been achieved by the coagulation-stripping process, in which instance large amounts of energy are required, in the form of Stripping vapor (wet process) Subsequently to this process step, the polymer needs to be separated from the stripping medium in a costly process of mechano-thermal drying. The removal of the stripping medium occurs in two phases by mechanical pressing out and atmospherical drying. During these processes, a great deal of energy in the form of water vapor and a great deal of cleaning water is required, leading to great volumes of waste water and, due to the large open aggregates, to high emissions. In parallel to said process, the stripping agent and the solvent need to be separated from each other, in yet another costly process. Consequently, the current procedure is very inefficient from an energy viewpoint, and a very ineffective technology characterized by high costs for emissions and investment. The existing technology is familiar, the risks are low and catalyst systems and the processing are adapted to this technology.
In the patent document U.S. Pat. No. 3,683,511, a method is described, which was especially developed for the degassing of polymer solutions containing polybutadiene and solutions in which more than 50% of butadiene is polymerized into the polymer. In accordance with the invention, the removal of the solvent is achieved by adding water into the extruder.
Similar problem solutions are also presented in U.S. Pat. No. 4,909,898 A and EP 0 262 594 B1. In these publications the polymer solution is brought into the mixer/kneader zone and the solvent is vaporized at the temperature at which the top surface of the heat transfer surface has a temperature higher than the boiling temperature of the solvent with the lowest boiling point. Also in this instance, a liquid which does not mix with the polymers is added, in this case water.
In U.S. Pat. No. 6,150,498 A and EP 0 910 588 B1, a process for degassing EPDM and similar polymers, such as polyethylene, polypropylene, ethylene-propylene rubber and polystyrol, with a thermal dryer is presented. In this instance, the thermal dryer consists of a horizontal jacket and a rotating shaft inside the jacket, plate elements which are positioned on the shaft, and stationary counter tangs tap positioned on the inner side of the jacket. The implementation of such a technology is confined to polymer solutions which are able to absorb larger amounts of dissipation energy, since the polymer would otherwise get too warm or the degassing performance would be insufficient.
Apart from the energy view point and the high emissions, especially the high costs, for water separation for the modern water sensitive anionic polymerization procedures and the treatment of extremely temperature sensitive products, are a driving force leading to the modernization of the procedure.
It is the objective of the invention to reduce the consumption of energy, i.e. water vapor, and of water, thus improving the energy balance of the process while enhancing the efficiency of new procedures. As a side effect, temperature sensitive mixed substances can be produced, as is not possible in the current technology, or rather only by adding special antioxidants. The new treatment procedure (dry process) is aimed at making the process more energy efficient, more environment friendly and more flexible.